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1. Field of the Invention
The invention relates to a method and an arrangement for improving leak tolerance in an earpiece of a radio device. The invention can be applied preferably in teleterminals, particularly in mobile stations.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Teleterminals conventionally contain a receiver part which has an earpiece for reproducing the received acoustic signal. The earpiece has been conventionally designed in such a way that it forms the maximum sound volume and the best quality of sound when the earpiece is sealed against the user""s ear. If there is a gap, i.e. a leak between the earpiece and the user""s ear, this usually causes a significant weakening of the sensed sound pressure. Additionally, the frequency distribution of the sensed sound does not then correspond to the original acoustic signal but low frequencies are attenuated to a greater extent than high frequencies. The ability of an earpiece to maintain its acoustic properties when the gap between the earpiece and the ear changes, is called its leak tolerance.
The problem described above is extremely serious particularly in mobile stations, because the mobile station is rarely completely sealed against the user""s ear. On the other hand, standards relating to mobile stations are primarily based on measurements where the gap between the mobile station and the artificial ear has been arranged so that there is a tight seal. In order to ensure that the volume and frequency distribution of the reproduced sound are according to specifications also in real operating conditions, extremely good leak tolerance is required from the earpiece arrangement.
To improve leak tolerance the following ways are prior known. The leak tolerance can be improved by arranging a loose coupling to the membrane which produces the sound waves in the earpiece capsule and by loading it by a relatively large volume situated behind the earpiece capsule. Most preferably the volume behind the earpiece capsule has been arranged to be open, in which case the aforementioned volume becomes as large as possible. Another way to improve the leak tolerance is to lower the acoustic output impedance of the arrangement by using an acoustic return path.
A disadvantage of the solutions according to prior art is that the load caused by the acoustic return path is difficult to optimize. The leak tolerance to be achieved depends essentially on the size of the volume arranged behind the earpiece capsule. In small-sized devices, such as mobile stations, it is difficult to provide a sufficiently large volume to achieve the optimum acoustic load, because the electronical units of the device occupy the volume within the casing of the device.
The aim of the present invention is to devise an earpiece solution which achieves good leak tolerance in a small-sized radio device, such as a mobile station.
One idea of the invention is that an acoustic volume is arranged behind the earpiece by taking advantage of the RF shield casing of the radio frequency unit of the device. The aim of the RF shield is to prevent radio frequency signals formed by a radio device, such as a mobile station, from entering the surroundings and to prevent disturbances in the RF circuits of the device caused by RF radiation which is present in the surroundings. According to the invention, an RF shielded volume of this kind is exploited as an acoustic volume loading the earpiece.
A particular advantage of the invention is that an acoustic volume which is loading the earpiece optimally can be formed behind the earpiece without it causing any necessary enlargement in the size of the device.
In one embodiment of the invention, one wall of the casing arranged behind the earpiece has been formed by means of an electronic circuit board to which circuit board radio frequency components of the electronic unit have been connected. Then between the casing and the external volume, an acoustic path can preferably be formed by means of through holes arranged in the circuit board.
A method according to the invention for improving leak tolerance in an earpiece of a radio device such that the sound formed by an earpiece capsule is directed from the front part of the earpiece capsule to the first acoustic volume which is confined by the user""s ear and the housing part between the earpiece capsule and the ear, is characterized in that the sound formed by the earpiece capsule is additionally directed from the back part of the earpiece capsule to a radio shielded volume of the radio device which is confined by a casing and operates as the second acoustic volume.
An arrangement according to the invention for improving leak tolerance of an earpiece in a radio device, which arrangement comprises
an earpiece capsule,
a housing part situated between the earpiece capsule and the user""s ear for confining the first acoustic volume between said housing part and user""s ear and
the first acoustic path arranged between the front part of the earpiece capsule and the first acoustic volume for directing sound from the front part of the earpiece capsule to said acoustic volume, is characterized in that it comprises additionally
a radio shielded volume confined by a casing and arranged for the RF parts of a radio device and
the second acoustic path for directing sound formed by the earpiece capsule from the back part of the earpiece capsule to said radio shielded volume.
A mobile station according to the invention, whose earpiece comprises
an earpiece capsule,
a housing part situated between the earpiece capsule and the user""s ear for confining the acoustic volume between said housing part and user""s ear and
the first acoustic path arranged between the front part of the earpiece capsule and said acoustic volume for directing sound from the front part of the earpiece capsule to said acoustic volume, is characterized in that the arrangement comprises additionally
a radio shielded volume confined by a casing and arranged for the RF parts of the mobile station and
the second acoustic path for directing sound formed by the earpiece capsule from the back part of the earpiece capsule to said radio shielded volume for improving the leak tolerance of the earpiece.
Preferable embodiments of the invention have been presented in dependent claims.
By the front and back parts of the earpiece capsule one means herein the front and back parts of a membrane which forms sound waves and is situated in the earpiece capsule, and sound waves generated in these front and back parts are in opposite phases from each other.
By the earpiece one means herein the earpiece capsule and acoustic and mechanical structures connected to it.